Search Results

You are looking at 1 - 10 of 42 items for

  • Author or Editor: K. A. Browning x
  • Refine by Access: All Content x
Clear All Modify Search
K. A. Browning

Abstract

Full access
K. A. Browning

Abstract

No abstract available.

Full access
K. A. Browning and D. Atlas

Abstract

It is suggested that progress in hail suppression research requires simultaneous improvements in methods of evaluating seeding effects and in monitoring the physical structure of the hailstorm and the hail growth processes. On this basis a case is made for the extensive use of multiple Doppler radar and chemical tracer techniques.

Full access
K. A. Browning and R. Wexler

Abstract

A technique is proposed for the measurement of kinematic properties of a wind field in situations of widespread precipitation, using a single Doppler radar to sense the motion of the precipitation particles. The technique is an extension of ideas put forward by Probert-Jones, Lhermitte, Atlas, Caton and Harrold, and is based upon the Velocity-Azimuth Display (VAD) obtained by scanning the radar beam about a vertical axis at a fixed elevation angle. Harmonic analysis of the VAD permits divergence to be obtained from the magnitude of the “zeroth” harmonic, wind speed and direction to be obtained from the amplitude and phase of the first harmonic, and resultant deformation and the axis of dilatation to be obtained from the amplitude and phase of the second harmonic. Although limitations to the accuracy of this technique are imposed by inhomogeneities in the horizontal distribution of precipitation fall speed and, in the presence of strong vertical wind shear, by elevation angle errors and reflectivity inhomogeneities, the errors resulting from these effects can be made acceptably small by scanning at appropriate elevation angles and ranges. An optimum scanning procedure is suggested. A short case study is also presented to support the view that meaningful estimates of mesoscale divergence and deformation can be obtained using this technique.

Full access
D. Chapman and K. A. Browning

The usefulness of displaying vertical wind shear on a radar range height indicator is demonstrated. Fine structure in the pattern of shear is shown to be helpful for inferring general flow patterns and the occurrence of billows due to shearing (Kelvin–Helmholtz) instability.

Full access
K. A. Browning and R. J. Donaldson

Abstract

The thunderstorm that produced tornadoes near Geary, Okla., on 4 May 1961 is analyzed using data mainly from a vertically-scanning FPS-6 radar. The storm configuration was remarkably similar in many respects to the severe Wokingham hailstorm in England, analyzed by Browning and Ludlam. Each attained a fairly steady state during which certain characteristic features were displayed. Most important of these was the vault, a region of low reflectivity beneath the highest parts of the storm which is believed to be symptomatic of an intense and persistent updraft. This and other features of its structure are analyzed in conjunction with nearby soundings to give a model of the airflow associated with the Geary storm. Like the Wokingham storm, it comprised a persistent updraft which entered and left on the downshear side. This kind of airflow is believed to be representative of an important class of persistently intense cumulonimbus which travel within a strongly sheared environment.

Full access
K. A. Browning, S. P. Ballard, and C. S. A. Davitt

Abstract

A mesoscale array of dropwindsondes, released in a small rapidly deepening frontal wave cyclone in the eastern North Atlantic during the FRONTS 92 experiment, has been assimilated into a 17-km-grid mesoscale model nested within the Meteorological Office’s operational Limited Area Model. The mesoscale model reproduced the evolving cloud pattern, with “cloud head” and “dry slot,” seen in satellite imagery. It also revealed a well-defined evolution in the three-dimensional thermodynamic structure associated with the process known as frontal fracture.

The frontal fracture was revealed most clearly in the pattern of wet-bulb potential temperature θ w, which was distorted by an effective differential rotation, the rotation increasing with height. This led to backward-tilted θ w surfaces (and ana-cold-frontal characteristics) in the cloud head to the north of the center of rotation, and to forward-tilted θ w surfaces (and kata-cold-frontal characteristics) in the dry slot to the south of the center of rotation. The effective differential rotation was associated with a local maximum of potential vorticity aloft within a developing tropopause fold.

Full access
J. Rosinski, K. A. Browning, G. Langer, and C. T. Nagamoto

Abstract

The distribution of water-insoluble aerosol particles with diameters in the range 3 to 60 (m has been studied as a function of hailstone radius for a collection of large hailstones. Most of the stones had opaque (probably graupel) embryos; a few had transparent (probably frozen drop) embryos. The concentration of particles within the opaque hailstone embryos was substantially smaller than the concentration of particles within the outer parts of the same hailstones, suggesting that the bulk of the hailstone growth had occurred in a different part of the storm from the region of embryo formation. It seems that the opaque embryos (graupel) form in weak updrafts and then grow into large haillstones upon entering an updraft core which is fed by dust-laden air originating closer to the ground. The transparent embryos were found to contain many more particles than the opaque embryos, perhaps indicating a different place of origin and also indicating an active role by the large particles ingested by a storm in the development of the transparent embryos.

Full access
K. A. Browning, J. Hallett, T. W. Harrold, and D. Johnson

Abstract

Attempts have been made to obtain samples of freshly fallen hailstones from severe storms in Oklahoma with the purpose of studying the nature and extent of spongy ice within natural hail. Interception by automobile of radar echoes with Ze > 105 mm6 m−3 has been found to provide a workable technique for collecting large hailstones as they fall to the ground. Observations suggest that the regions of highest reflectivity were associated more closely with the falls of large hail than with the accompanying heavy rain.

Immediate sectioning of the freshly fallen hailstones revealed the presence of thin shells of spongy ice in many of the larger stones. Calorimetric analyses gave liquid water contents of up to 12 ± 4% of the mass of the stones. Some of the hailstones were aspherical owing to preferential melting of the regions of spongy ice during fall. In the case of hailstones that were stored at sub-freezing temperatures, spongy ice shells could often still be identified from the presence of millimeter size cavities embedded within ice composed of large crystals.

Full access
A. R. Brown, M. K. MacVean, and P. J. Mason

Abstract

Large eddy simulations sometimes use monotone advection schemes. Such schemes are dissipative, and the effective subgrid model then becomes the combined effect of the intended model and of the numerical dissipation. The impacts on simulation reliability are examined for the cases of dry convective and neutral planetary boundary layers. In general it is found that the results in the well-resolved flow interior are insensitive to the details of the advection scheme. However, unsatisfactory results may be obtained if numerical dissipation dominates where the flow becomes less well resolved as the surface is approached.

Full access